Abstract

We demonstrate that the polarization patterns observed in backscattering of linearly polarized light are a manifestation of the conservation of angular momentum of light. We will show that this phenomenon can be described in terms of phase vortices that are acquired by the right and left circularly polarized components. The helicity and orbital angular momentum of these components satisfy the requirement for conservation of angular momentum.

Figures (2)

Polarization distribution obtained by superposing a right circularly polarized phase vortex (with a topological charge equal to −2) and a left circular phase vortex (with a topological charge equal to 2). (a) Intensity image, where the vectors indicate the electric field direction. (b) Intensity distribution after a horizontal linear analyzer that is proportional to cos2(2ϕ), where ϕ is the azimuth angle. (c) Intensity distribution after a vertical linear analyzer that is proportional to sin2(2ϕ).

(Color online) Scattering paths illustrated (a) in real space and (b) in k space. In k space the path describes the locations of the tip of the k vectors after each scattering event (they all lie on the surface of a sphere, since the scattering considered is elastic). A planar nearly semicircular path in real space will have a corresponding path in k space that is a geodesic, starting at the forward pole and ending at the backward pole. The geometric phase corresponding to this path is the solid angle subtended between the actual path and the reference path, as indicated.